feat(ext/ffi): structs by value (#15060)

Adds support for passing and returning structs as buffers to FFI. This does not implement fastapi support for structs. Needed for certain system APIs such as AppKit on macOS.

Cargo.lock

@@ -2557,9 +2557,9 @@ checksum = "349d5a591cd28b49e1d1037471617a32ddcda5731b99419008085f72d5a53836"
 
 [[package]]
 name = "libffi"
-version = "3.0.1"
+version = "3.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1e454b3efb16fba3b17810ae5e41df02b649e564ab3c5a34b3b93ed07ad287e6"
+checksum = "6cb06d5b4c428f3cd682943741c39ed4157ae989fffe1094a08eaf7c4014cf60"
 dependencies = [
  "libc",
  "libffi-sys",
@@ -2567,9 +2567,9 @@ dependencies = [
 
 [[package]]
 name = "libffi-sys"
-version = "2.0.0"
+version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab4106b7f09d7b87d021334d5618fac1dfcfb824d4c5fe111ff0074dfd242e15"
+checksum = "11c6f11e063a27ffe040a9d15f0b661bf41edc2383b7ae0e0ad5a7e7d53d9da3"
 dependencies = [
  "cc",
 ]

cli/tsc/dts/lib.deno.unstable.d.ts

@@ -94,6 +94,13 @@ declare namespace Deno {
    */
   type NativeVoidType = "void";
 
+  /** **UNSTABLE**: New API, yet to be vetted.
+   * 
+   * The native struct type for interfacing with foreign functions.
+   * 
+   */
+  type NativeStructType = { readonly struct: readonly NativeType[] };
+
   /** **UNSTABLE**: New API, yet to be vetted.
    *
    * All supported types for interfacing with foreign functions.
@@ -106,7 +113,8 @@ declare namespace Deno {
     | NativeBooleanType
     | NativePointerType
     | NativeBufferType
-    | NativeFunctionType;
+    | NativeFunctionType
+    | NativeStructType;
 
   /** **UNSTABLE**: New API, yet to be vetted.
    *
@@ -136,7 +144,9 @@ declare namespace Deno {
    *
    * @category FFI
    */
-  type ToNativeType<T extends NativeType = NativeType> = ToNativeTypeMap[T];
+  type ToNativeType<T extends NativeType = NativeType> = T extends
+    NativeStructType ? BufferSource
+    : ToNativeTypeMap[Exclude<T, NativeStructType>];
 
   /** **UNSTABLE**: New API, yet to be vetted.
    *
@@ -153,7 +163,8 @@ declare namespace Deno {
    * @category FFI
    */
   type ToNativeResultType<T extends NativeResultType = NativeResultType> =
-    ToNativeResultTypeMap[T];
+    T extends NativeStructType ? BufferSource
+    : ToNativeResultTypeMap[Exclude<T, NativeStructType>];
 
   /** **UNSTABLE**: New API, yet to be vetted.
    *
@@ -193,7 +204,9 @@ declare namespace Deno {
    *
    * @category FFI
    */
-  type FromNativeType<T extends NativeType = NativeType> = FromNativeTypeMap[T];
+  type FromNativeType<T extends NativeType = NativeType> = T extends
+    NativeStructType ? Uint8Array
+    : FromNativeTypeMap[Exclude<T, NativeStructType>];
 
   /** **UNSTABLE**: New API, yet to be vetted.
    *
@@ -212,7 +225,8 @@ declare namespace Deno {
    * @category FFI
    */
   type FromNativeResultType<T extends NativeResultType = NativeResultType> =
-    FromNativeResultTypeMap[T];
+    T extends NativeStructType ? Uint8Array
+    : FromNativeResultTypeMap[Exclude<T, NativeStructType>];
 
   /** **UNSTABLE**: New API, yet to be vetted.
    *

ext/ffi/00_ffi.js

@@ -14,12 +14,18 @@
     Number,
     NumberIsSafeInteger,
     TypeError,
+    Uint8Array,
     Int32Array,
     Uint32Array,
     BigInt64Array,
     BigUint64Array,
     Function,
     ReflectHas,
+    PromisePrototypeThen,
+    MathMax,
+    MathCeil,
+    Map,
+    SafeArrayIterator,
   } = window.__bootstrap.primordials;
 
   const U32_BUFFER = new Uint32Array(2);
@@ -181,26 +187,55 @@
   class UnsafeFnPointer {
     pointer;
     definition;
+    #structSize;
 
     constructor(pointer, definition) {
       this.pointer = pointer;
       this.definition = definition;
+      this.#structSize = isStruct(definition.result)
+        ? getTypeSizeAndAlignment(definition.result)[0]
+        : null;
     }
 
     call(...parameters) {
       if (this.definition.nonblocking) {
-        return core.opAsync(
+        if (this.#structSize === null) {
-          "op_ffi_call_ptr_nonblocking",
+          return core.opAsync(
-          this.pointer,
+            "op_ffi_call_ptr_nonblocking",
-          this.definition,
+            this.pointer,
-          parameters,
+            this.definition,
-        );
+            parameters,
+          );
+        } else {
+          const buffer = new Uint8Array(this.#structSize);
+          return PromisePrototypeThen(
+            core.opAsync(
+              "op_ffi_call_ptr_nonblocking",
+              this.pointer,
+              this.definition,
+              parameters,
+              buffer,
+            ),
+            () => buffer,
+          );
+        }
       } else {
-        return ops.op_ffi_call_ptr(
+        if (this.#structSize === null) {
-          this.pointer,
+          return ops.op_ffi_call_ptr(
-          this.definition,
+            this.pointer,
-          parameters,
+            this.definition,
-        );
+            parameters,
+          );
+        } else {
+          const buffer = new Uint8Array(this.#structSize);
+          ops.op_ffi_call_ptr(
+            this.pointer,
+            this.definition,
+            parameters,
+            buffer,
+          );
+          return buffer;
+        }
       }
     }
   }
@@ -215,6 +250,60 @@
     return type === "i64" || type === "isize";
   }
 
+  function isStruct(type) {
+    return typeof type === "object" && type !== null &&
+      typeof type.struct === "object";
+  }
+
+  function getTypeSizeAndAlignment(type, cache = new Map()) {
+    if (isStruct(type)) {
+      const cached = cache.get(type);
+      if (cached !== undefined) {
+        if (cached === null) {
+          throw new TypeError("Recursive struct definition");
+        }
+        return cached;
+      }
+      cache.set(type, null);
+      let size = 0;
+      let alignment = 1;
+      for (const field of new SafeArrayIterator(type.struct)) {
+        const [fieldSize, fieldAlign] = getTypeSizeAndAlignment(field, cache);
+        alignment = MathMax(alignment, fieldAlign);
+        size = MathCeil(size / fieldAlign) * fieldAlign;
+        size += fieldSize;
+      }
+      size = MathCeil(size / alignment) * alignment;
+      cache.set(type, size);
+      return [size, alignment];
+    }
+
+    switch (type) {
+      case "bool":
+      case "u8":
+      case "i8":
+        return [1, 1];
+      case "u16":
+      case "i16":
+        return [2, 2];
+      case "u32":
+      case "i32":
+      case "f32":
+        return [4, 4];
+      case "u64":
+      case "i64":
+      case "f64":
+      case "pointer":
+      case "buffer":
+      case "function":
+      case "usize":
+      case "isize":
+        return [8, 8];
+      default:
+        throw new TypeError(`Unsupported type: ${type}`);
+    }
+  }
+
   class UnsafeCallback {
     #refcount;
     // Internal promise only meant to keep Deno from exiting
@@ -306,6 +395,10 @@
           continue;
         }
         const resultType = symbols[symbol].result;
+        const isStructResult = isStruct(resultType);
+        const structSize = isStructResult
+          ? getTypeSizeAndAlignment(resultType)[0]
+          : 0;
         const needsUnpacking = isReturnedAsBigInt(resultType);
 
         const isNonBlocking = symbols[symbol].nonblocking;
@@ -317,12 +410,27 @@
               configurable: false,
               enumerable: true,
               value: (...parameters) => {
-                return core.opAsync(
+                if (isStructResult) {
-                  "op_ffi_call_nonblocking",
+                  const buffer = new Uint8Array(structSize);
-                  this.#rid,
+                  const ret = core.opAsync(
-                  symbol,
+                    "op_ffi_call_nonblocking",
-                  parameters,
+                    this.#rid,
-                );
+                    symbol,
+                    parameters,
+                    buffer,
+                  );
+                  return PromisePrototypeThen(
+                    ret,
+                    () => buffer,
+                  );
+                } else {
+                  return core.opAsync(
+                    "op_ffi_call_nonblocking",
+                    this.#rid,
+                    symbol,
+                    parameters,
+                  );
+                }
               },
               writable: false,
             },
@@ -359,6 +467,21 @@
             return b[0];
           }`,
           )(vi, vui, b, call, NumberIsSafeInteger, Number);
+        } else if (isStructResult && !isNonBlocking) {
+          const call = this.symbols[symbol];
+          const parameters = symbols[symbol].parameters;
+          const params = ArrayPrototypeJoin(
+            ArrayPrototypeMap(parameters, (_, index) => `p${index}`),
+            ", ",
+          );
+          this.symbols[symbol] = new Function(
+            "call",
+            `return function (${params}) {
+            const buffer = new Uint8Array(${structSize});
+            call(${params}${parameters.length > 0 ? ", " : ""}buffer);
+            return buffer;
+          }`,
+          )(call);
         }
       }
     }

ext/ffi/Cargo.toml

@@ -17,7 +17,7 @@ path = "lib.rs"
 deno_core.workspace = true
 dlopen.workspace = true
 dynasmrt = "1.2.3"
-libffi = "3.0.0"
+libffi = "3.1.0"
 serde.workspace = true
 tokio.workspace = true
 

ext/ffi/call.rs

@@ -22,11 +22,28 @@ use std::ffi::c_void;
 use std::future::Future;
 use std::rc::Rc;
 
+// SAFETY: Makes an FFI call
+unsafe fn ffi_call_rtype_struct(
+  cif: &libffi::middle::Cif,
+  fn_ptr: &libffi::middle::CodePtr,
+  call_args: Vec<Arg>,
+  out_buffer: *mut u8,
+) -> NativeValue {
+  libffi::raw::ffi_call(
+    cif.as_raw_ptr(),
+    Some(*fn_ptr.as_safe_fun()),
+    out_buffer as *mut c_void,
+    call_args.as_ptr() as *mut *mut c_void,
+  );
+  NativeValue { void_value: () }
+}
+
 // A one-off synchronous FFI call.
 pub(crate) fn ffi_call_sync<'scope>(
   scope: &mut v8::HandleScope<'scope>,
   args: v8::FunctionCallbackArguments,
   symbol: &Symbol,
+  out_buffer: Option<OutBuffer>,
 ) -> Result<NativeValue, AnyError>
 where
   'scope: 'scope,
@@ -86,6 +103,9 @@ where
       NativeType::Buffer => {
         ffi_args.push(ffi_parse_buffer_arg(scope, value)?);
       }
+      NativeType::Struct(_) => {
+        ffi_args.push(ffi_parse_struct_arg(scope, value)?);
+      }
       NativeType::Pointer => {
         ffi_args.push(ffi_parse_pointer_arg(scope, value)?);
       }
@@ -97,7 +117,12 @@ where
       }
     }
   }
-  let call_args: Vec<Arg> = ffi_args.iter().map(Arg::new).collect();
+  let call_args: Vec<Arg> = ffi_args
+    .iter()
+    .enumerate()
+    // SAFETY: Creating a `Arg` from a `NativeValue` is pretty safe.
+    .map(|(i, v)| unsafe { v.as_arg(parameter_types.get(i).unwrap()) })
+    .collect();
   // SAFETY: types in the `Cif` match the actual calling convention and
   // types of symbol.
   unsafe {
@@ -149,6 +174,12 @@ where
           pointer: cif.call::<*mut c_void>(*fun_ptr, &call_args),
         }
       }
+      NativeType::Struct(_) => ffi_call_rtype_struct(
+        &symbol.cif,
+        &symbol.ptr,
+        call_args,
+        out_buffer.unwrap().0,
+      ),
     })
   }
 }
@@ -159,13 +190,14 @@ fn ffi_call(
   fun_ptr: libffi::middle::CodePtr,
   parameter_types: &[NativeType],
   result_type: NativeType,
+  out_buffer: Option<OutBuffer>,
 ) -> Result<NativeValue, AnyError> {
   let call_args: Vec<Arg> = call_args
     .iter()
     .enumerate()
     .map(|(index, ffi_arg)| {
       // SAFETY: the union field is initialized
-      unsafe { ffi_arg.as_arg(*parameter_types.get(index).unwrap()) }
+      unsafe { ffi_arg.as_arg(parameter_types.get(index).unwrap()) }
     })
     .collect();
 
@@ -220,6 +252,9 @@ fn ffi_call(
           pointer: cif.call::<*mut c_void>(fun_ptr, &call_args),
         }
       }
+      NativeType::Struct(_) => {
+        ffi_call_rtype_struct(cif, &fun_ptr, call_args, out_buffer.unwrap().0)
+      }
     })
   }
 }
@@ -231,6 +266,7 @@ pub fn op_ffi_call_ptr_nonblocking<'scope, FP>(
   pointer: usize,
   def: ForeignFunction,
   parameters: serde_v8::Value<'scope>,
+  out_buffer: Option<serde_v8::Value<'scope>>,
 ) -> Result<impl Future<Output = Result<Value, AnyError>>, AnyError>
 where
   FP: FfiPermissions + 'static,
@@ -244,10 +280,22 @@ where
 
   let symbol = PtrSymbol::new(pointer, &def);
   let call_args = ffi_parse_args(scope, parameters, &def.parameters)?;
+  let def_result = def.result.clone();
+
+  let out_buffer = out_buffer
+    .map(|v| v8::Local::<v8::TypedArray>::try_from(v.v8_value).unwrap());
+  let out_buffer_ptr = out_buffer_as_ptr(scope, out_buffer);
 
   let join_handle = tokio::task::spawn_blocking(move || {
     let PtrSymbol { cif, ptr } = symbol.clone();
-    ffi_call(call_args, &cif, ptr, &def.parameters, def.result)
+    ffi_call(
+      call_args,
+      &cif,
+      ptr,
+      &def.parameters,
+      def.result,
+      out_buffer_ptr,
+    )
   });
 
   Ok(async move {
@@ -255,7 +303,7 @@ where
       .await
       .map_err(|err| anyhow!("Nonblocking FFI call failed: {}", err))??;
     // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
-    Ok(unsafe { result.to_value(def.result) })
+    Ok(unsafe { result.to_value(def_result) })
   })
 }
 
@@ -267,6 +315,7 @@ pub fn op_ffi_call_nonblocking<'scope>(
   rid: ResourceId,
   symbol: String,
   parameters: serde_v8::Value<'scope>,
+  out_buffer: Option<serde_v8::Value<'scope>>,
 ) -> Result<impl Future<Output = Result<Value, AnyError>> + 'static, AnyError> {
   let symbol = {
     let state = state.borrow();
@@ -279,8 +328,11 @@ pub fn op_ffi_call_nonblocking<'scope>(
   };
 
   let call_args = ffi_parse_args(scope, parameters, &symbol.parameter_types)?;
+  let out_buffer = out_buffer
+    .map(|v| v8::Local::<v8::TypedArray>::try_from(v.v8_value).unwrap());
+  let out_buffer_ptr = out_buffer_as_ptr(scope, out_buffer);
 
-  let result_type = symbol.result_type;
+  let result_type = symbol.result_type.clone();
   let join_handle = tokio::task::spawn_blocking(move || {
     let Symbol {
       cif,
@@ -289,7 +341,14 @@ pub fn op_ffi_call_nonblocking<'scope>(
       result_type,
       ..
     } = symbol.clone();
-    ffi_call(call_args, &cif, ptr, &parameter_types, result_type)
+    ffi_call(
+      call_args,
+      &cif,
+      ptr,
+      &parameter_types,
+      result_type,
+      out_buffer_ptr,
+    )
   });
 
   Ok(async move {
@@ -308,6 +367,7 @@ pub fn op_ffi_call_ptr<FP, 'scope>(
   pointer: usize,
   def: ForeignFunction,
   parameters: serde_v8::Value<'scope>,
+  out_buffer: Option<serde_v8::Value<'scope>>,
 ) -> Result<serde_v8::Value<'scope>, AnyError>
 where
   FP: FfiPermissions + 'static,
@@ -322,12 +382,17 @@ where
   let symbol = PtrSymbol::new(pointer, &def);
   let call_args = ffi_parse_args(scope, parameters, &def.parameters)?;
 
+  let out_buffer = out_buffer
+    .map(|v| v8::Local::<v8::TypedArray>::try_from(v.v8_value).unwrap());
+  let out_buffer_ptr = out_buffer_as_ptr(scope, out_buffer);
+
   let result = ffi_call(
     call_args,
     &symbol.cif,
     symbol.ptr,
     &def.parameters,
-    def.result,
+    def.result.clone(),
+    out_buffer_ptr,
   )?;
   // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
   let result = unsafe { result.to_v8(scope, def.result) };

ext/ffi/callback.rs

@@ -48,7 +48,7 @@ impl PtrSymbol {
         .clone()
         .into_iter()
         .map(libffi::middle::Type::from),
-      def.result.into(),
+      def.result.clone().into(),
     );
 
     Self { cif, ptr }
@@ -113,7 +113,7 @@ impl Future for CallbackInfo {
   }
 }
 unsafe extern "C" fn deno_ffi_callback(
-  _cif: &libffi::low::ffi_cif,
+  cif: &libffi::low::ffi_cif,
   result: &mut c_void,
   args: *const *const c_void,
   info: &CallbackInfo,
@@ -121,15 +121,16 @@ unsafe extern "C" fn deno_ffi_callback(
   LOCAL_ISOLATE_POINTER.with(|s| {
     if ptr::eq(*s.borrow(), info.isolate) {
       // Own isolate thread, okay to call directly
-      do_ffi_callback(info, result, args);
+      do_ffi_callback(cif, info, result, args);
     } else {
       let async_work_sender = &info.async_work_sender;
       // SAFETY: Safe as this function blocks until `do_ffi_callback` completes and a response message is received.
+      let cif: &'static libffi::low::ffi_cif = std::mem::transmute(cif);
       let result: &'static mut c_void = std::mem::transmute(result);
       let info: &'static CallbackInfo = std::mem::transmute(info);
       let (response_sender, response_receiver) = sync_channel::<()>(0);
       let fut = Box::new(move || {
-        do_ffi_callback(info, result, args);
+        do_ffi_callback(cif, info, result, args);
         response_sender.send(()).unwrap();
       });
       async_work_sender.unbounded_send(fut).unwrap();
@@ -143,6 +144,7 @@ unsafe extern "C" fn deno_ffi_callback(
 }
 
 unsafe fn do_ffi_callback(
+  cif: &libffi::low::ffi_cif,
   info: &CallbackInfo,
   result: &mut c_void,
   args: *const *const c_void,
@@ -172,9 +174,12 @@ unsafe fn do_ffi_callback(
   let result = result as *mut c_void;
   let vals: &[*const c_void] =
     std::slice::from_raw_parts(args, info.parameters.len());
+  let arg_types = std::slice::from_raw_parts(cif.arg_types, cif.nargs as usize);
 
   let mut params: Vec<v8::Local<v8::Value>> = vec![];
-  for (native_type, val) in info.parameters.iter().zip(vals) {
+  for ((index, native_type), val) in
+    info.parameters.iter().enumerate().zip(vals)
+  {
     let value: v8::Local<v8::Value> = match native_type {
       NativeType::Bool => {
         let value = *((*val) as *const bool);
@@ -237,6 +242,20 @@ unsafe fn do_ffi_callback(
           v8::Number::new(scope, result as f64).into()
         }
       }
+      NativeType::Struct(_) => {
+        let size = arg_types[index].as_ref().unwrap().size;
+        let ptr = (*val) as *const u8;
+        let slice = std::slice::from_raw_parts(ptr, size);
+        let boxed = Box::from(slice);
+        let store = v8::ArrayBuffer::new_backing_store_from_boxed_slice(boxed);
+        let ab =
+          v8::ArrayBuffer::with_backing_store(scope, &store.make_shared());
+        let local_value: v8::Local<v8::Value> =
+          v8::Uint8Array::new(scope, ab, 0, ab.byte_length())
+            .unwrap()
+            .into();
+        local_value
+      }
       NativeType::Void => unreachable!(),
     };
     params.push(value);
@@ -440,6 +459,35 @@ unsafe fn do_ffi_callback(
           as u64;
       }
     }
+    NativeType::Struct(_) => {
+      let size;
+      let pointer = if let Ok(value) =
+        v8::Local::<v8::ArrayBufferView>::try_from(value)
+      {
+        let byte_offset = value.byte_offset();
+        let ab = value
+          .buffer(scope)
+          .expect("Unable to deserialize result parameter.");
+        size = value.byte_length();
+        ab.data()
+          .expect("Unable to deserialize result parameter.")
+          .as_ptr()
+          .add(byte_offset)
+      } else if let Ok(value) = v8::Local::<v8::ArrayBuffer>::try_from(value) {
+        size = value.byte_length();
+        value
+          .data()
+          .expect("Unable to deserialize result parameter.")
+          .as_ptr()
+      } else {
+        panic!("Unable to deserialize result parameter.");
+      };
+      std::ptr::copy_nonoverlapping(
+        pointer as *mut u8,
+        result as *mut u8,
+        std::cmp::min(size, (*cif.rtype).size),
+      );
+    }
     NativeType::Void => {
       // nop
     }
@@ -522,7 +570,7 @@ where
 
   let info: *mut CallbackInfo = Box::leak(Box::new(CallbackInfo {
     parameters: args.parameters.clone(),
-    result: args.result,
+    result: args.result.clone(),
     async_work_sender,
     callback,
     context,

ext/ffi/dlfcn.rs

@@ -1,6 +1,7 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 
 use crate::check_unstable;
+use crate::ir::out_buffer_as_ptr;
 use crate::symbol::NativeType;
 use crate::symbol::Symbol;
 use crate::turbocall;
@@ -52,7 +53,7 @@ impl DynamicLibraryResource {
   }
 }
 
-pub fn needs_unwrap(rv: NativeType) -> bool {
+pub fn needs_unwrap(rv: &NativeType) -> bool {
   matches!(
     rv,
     NativeType::Function
@@ -65,7 +66,7 @@ pub fn needs_unwrap(rv: NativeType) -> bool {
   )
 }
 
-fn is_i64(rv: NativeType) -> bool {
+fn is_i64(rv: &NativeType) -> bool {
   matches!(rv, NativeType::I64 | NativeType::ISize)
 }
 
@@ -166,7 +167,7 @@ where
             .clone()
             .into_iter()
             .map(libffi::middle::Type::from),
-          foreign_fn.result.into(),
+          foreign_fn.result.clone().into(),
         );
 
         let func_key = v8::String::new(scope, &symbol_key).unwrap();
@@ -216,11 +217,24 @@ fn make_sync_fn<'s>(
       // SAFETY: The pointer will not be deallocated until the function is
       // garbage collected.
       let symbol = unsafe { &*(external.value() as *const Symbol) };
-      let needs_unwrap = match needs_unwrap(symbol.result_type) {
+      let needs_unwrap = match needs_unwrap(&symbol.result_type) {
         true => Some(args.get(symbol.parameter_types.len() as i32)),
         false => None,
       };
-      match crate::call::ffi_call_sync(scope, args, symbol) {
+      let out_buffer = match symbol.result_type {
+        NativeType::Struct(_) => {
+          let argc = args.length();
+          out_buffer_as_ptr(
+            scope,
+            Some(
+              v8::Local::<v8::TypedArray>::try_from(args.get(argc - 1))
+                .unwrap(),
+            ),
+          )
+        }
+        _ => None,
+      };
+      match crate::call::ffi_call_sync(scope, args, symbol, out_buffer) {
         Ok(result) => {
           match needs_unwrap {
             Some(v) => {
@@ -228,7 +242,7 @@ fn make_sync_fn<'s>(
               let backing_store =
                 view.buffer(scope).unwrap().get_backing_store();
 
-              if is_i64(symbol.result_type) {
+              if is_i64(&symbol.result_type) {
                 // SAFETY: v8::SharedRef<v8::BackingStore> is similar to Arc<[u8]>,
                 // it points to a fixed continuous slice of bytes on the heap.
                 let bs = unsafe {
@@ -251,8 +265,9 @@ fn make_sync_fn<'s>(
               }
             }
             None => {
-              // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
+              let result =
-              let result = unsafe { result.to_v8(scope, symbol.result_type) };
+                // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
+                unsafe { result.to_v8(scope, symbol.result_type.clone()) };
               rv.set(result.v8_value);
             }
           }

ext/ffi/ir.rs

@@ -12,6 +12,29 @@ use libffi::middle::Arg;
 use std::ffi::c_void;
 use std::ptr;
 
+pub struct OutBuffer(pub *mut u8, pub usize);
+
+// SAFETY: OutBuffer is allocated by us in 00_ffi.js and is guaranteed to be
+// only used for the purpose of writing return value of structs.
+unsafe impl Send for OutBuffer {}
+// SAFETY: See above
+unsafe impl Sync for OutBuffer {}
+
+pub fn out_buffer_as_ptr(
+  scope: &mut v8::HandleScope,
+  out_buffer: Option<v8::Local<v8::TypedArray>>,
+) -> Option<OutBuffer> {
+  match out_buffer {
+    Some(out_buffer) => {
+      let ab = out_buffer.buffer(scope).unwrap();
+      let len = ab.byte_length();
+      ab.data()
+        .map(|non_null| OutBuffer(non_null.as_ptr() as *mut u8, len))
+    }
+    None => None,
+  }
+}
+
 /// Intermediate format for easy translation from NativeType + V8 value
 /// to libffi argument types.
 #[repr(C)]
@@ -34,7 +57,7 @@ pub union NativeValue {
 }
 
 impl NativeValue {
-  pub unsafe fn as_arg(&self, native_type: NativeType) -> Arg {
+  pub unsafe fn as_arg(&self, native_type: &NativeType) -> Arg {
     match native_type {
       NativeType::Void => unreachable!(),
       NativeType::Bool => Arg::new(&self.bool_value),
@@ -53,6 +76,7 @@ impl NativeValue {
       NativeType::Pointer | NativeType::Buffer | NativeType::Function => {
         Arg::new(&self.pointer)
       }
+      NativeType::Struct(_) => Arg::new(&*self.pointer),
     }
   }
 
@@ -76,6 +100,10 @@ impl NativeValue {
       NativeType::Pointer | NativeType::Function | NativeType::Buffer => {
         Value::from(self.pointer as usize)
       }
+      NativeType::Struct(_) => {
+        // Return value is written to out_buffer
+        Value::Null
+      }
     }
   }
 
@@ -187,6 +215,10 @@ impl NativeValue {
           };
         local_value.into()
       }
+      NativeType::Struct(_) => {
+        let local_value: v8::Local<v8::Value> = v8::null(scope).into();
+        local_value.into()
+      }
     }
   }
 }
@@ -426,6 +458,48 @@ pub fn ffi_parse_buffer_arg(
   Ok(NativeValue { pointer })
 }
 
+#[inline]
+pub fn ffi_parse_struct_arg(
+  scope: &mut v8::HandleScope,
+  arg: v8::Local<v8::Value>,
+) -> Result<NativeValue, AnyError> {
+  // Order of checking:
+  // 1. ArrayBuffer: Fairly common and not supported by Fast API, optimise this case.
+  // 2. ArrayBufferView: Common and supported by Fast API
+
+  let pointer = if let Ok(value) = v8::Local::<v8::ArrayBuffer>::try_from(arg) {
+    if let Some(non_null) = value.data() {
+      non_null.as_ptr()
+    } else {
+      return Err(type_error(
+        "Invalid FFI ArrayBuffer, expected data in buffer",
+      ));
+    }
+  } else if let Ok(value) = v8::Local::<v8::ArrayBufferView>::try_from(arg) {
+    let byte_offset = value.byte_offset();
+    let pointer = value
+      .buffer(scope)
+      .ok_or_else(|| {
+        type_error("Invalid FFI ArrayBufferView, expected data in the buffer")
+      })?
+      .data();
+    if let Some(non_null) = pointer {
+      // SAFETY: Pointer is non-null, and V8 guarantees that the byte_offset
+      // is within the buffer backing store.
+      unsafe { non_null.as_ptr().add(byte_offset) }
+    } else {
+      return Err(type_error(
+        "Invalid FFI ArrayBufferView, expected data in buffer",
+      ));
+    }
+  } else {
+    return Err(type_error(
+      "Invalid FFI struct type, expected ArrayBuffer, or ArrayBufferView",
+    ));
+  };
+  Ok(NativeValue { pointer })
+}
+
 #[inline]
 pub fn ffi_parse_function_arg(
   scope: &mut v8::HandleScope,
@@ -511,6 +585,9 @@ where
       NativeType::Buffer => {
         ffi_args.push(ffi_parse_buffer_arg(scope, value)?);
       }
+      NativeType::Struct(_) => {
+        ffi_args.push(ffi_parse_struct_arg(scope, value)?);
+      }
       NativeType::Pointer => {
         ffi_args.push(ffi_parse_pointer_arg(scope, value)?);
       }

ext/ffi/static.rs

@@ -142,5 +142,8 @@ pub fn op_ffi_get_static<'scope>(
       };
       integer.into()
     }
+    NativeType::Struct(_) => {
+      return Err(type_error("Invalid FFI static type 'struct'"));
+    }
   })
 }

ext/ffi/symbol.rs

@@ -2,7 +2,7 @@
 
 /// Defines the accepted types that can be used as
 /// parameters and return values in FFI.
-#[derive(Clone, Copy, Debug, serde::Deserialize, Eq, PartialEq)]
+#[derive(Clone, Debug, serde::Deserialize, Eq, PartialEq)]
 #[serde(rename_all = "lowercase")]
 pub enum NativeType {
   Void,
@@ -22,6 +22,7 @@ pub enum NativeType {
   Pointer,
   Buffer,
   Function,
+  Struct(Box<[NativeType]>),
 }
 
 impl From<NativeType> for libffi::middle::Type {
@@ -43,6 +44,9 @@ impl From<NativeType> for libffi::middle::Type {
       NativeType::Pointer | NativeType::Buffer | NativeType::Function => {
         libffi::middle::Type::pointer()
       }
+      NativeType::Struct(fields) => libffi::middle::Type::structure(
+        fields.iter().map(|field| field.clone().into()),
+      ),
     }
   }
 }

ext/ffi/turbocall.rs

@@ -14,11 +14,17 @@ use crate::NativeType;
 use crate::Symbol;
 
 pub(crate) fn is_compatible(sym: &Symbol) -> bool {
+  // TODO: Support structs by value in fast call
   cfg!(any(
     all(target_arch = "x86_64", target_family = "unix"),
     all(target_arch = "x86_64", target_family = "windows"),
     all(target_arch = "aarch64", target_vendor = "apple")
   )) && !sym.can_callback
+    && !matches!(sym.result_type, NativeType::Struct(_))
+    && !sym
+      .parameter_types
+      .iter()
+      .any(|t| matches!(t, NativeType::Struct(_)))
 }
 
 pub(crate) fn compile_trampoline(sym: &Symbol) -> Trampoline {
@@ -39,7 +45,7 @@ pub(crate) fn make_template(sym: &Symbol, trampoline: &Trampoline) -> Template {
     .chain(sym.parameter_types.iter().map(|t| t.into()))
     .collect::<Vec<_>>();
 
-  let ret = if needs_unwrap(sym.result_type) {
+  let ret = if needs_unwrap(&sym.result_type) {
     params.push(fast_api::Type::TypedArray(fast_api::CType::Int32));
     fast_api::Type::Void
   } else {
@@ -104,6 +110,9 @@ impl From<&NativeType> for fast_api::Type {
         fast_api::Type::Uint64
       }
       NativeType::Buffer => fast_api::Type::TypedArray(fast_api::CType::Uint8),
+      NativeType::Struct(_) => {
+        fast_api::Type::TypedArray(fast_api::CType::Uint8)
+      }
     }
   }
 }
@@ -161,9 +170,9 @@ impl SysVAmd64 {
     let mut compiler = Self::new();
 
     let must_cast_return_value =
-      compiler.must_cast_return_value(sym.result_type);
+      compiler.must_cast_return_value(&sym.result_type);
     let must_wrap_return_value =
-      compiler.must_wrap_return_value_in_typed_array(sym.result_type);
+      compiler.must_wrap_return_value_in_typed_array(&sym.result_type);
     let must_save_preserved_register = must_wrap_return_value;
     let cannot_tailcall = must_cast_return_value || must_wrap_return_value;
 
@@ -174,7 +183,7 @@ impl SysVAmd64 {
       compiler.allocate_stack(&sym.parameter_types);
     }
 
-    for param in sym.parameter_types.iter().copied() {
+    for param in sym.parameter_types.iter().cloned() {
       compiler.move_left(param)
     }
     if !compiler.is_recv_arg_overridden() {
@@ -188,7 +197,7 @@ impl SysVAmd64 {
     if cannot_tailcall {
       compiler.call(sym.ptr.as_ptr());
       if must_cast_return_value {
-        compiler.cast_return_value(sym.result_type);
+        compiler.cast_return_value(&sym.result_type);
       }
       if must_wrap_return_value {
         compiler.wrap_return_value_in_out_array();
@@ -400,7 +409,7 @@ impl SysVAmd64 {
     );
   }
 
-  fn cast_return_value(&mut self, rv: NativeType) {
+  fn cast_return_value(&mut self, rv: &NativeType) {
     let s = &mut self.assmblr;
     // V8 only supports 32bit integers. We support 8 and 16 bit integers casting them to 32bits.
     // In SysV-AMD64 the convention dictates that the unused bits of the return value contain garbage, so we
@@ -550,7 +559,7 @@ impl SysVAmd64 {
     self.integral_params > 0
   }
 
-  fn must_cast_return_value(&self, rv: NativeType) -> bool {
+  fn must_cast_return_value(&self, rv: &NativeType) -> bool {
     // V8 only supports i32 and u32 return types for integers
     // We support 8 and 16 bit integers by extending them to 32 bits in the trampoline before returning
     matches!(
@@ -559,7 +568,7 @@ impl SysVAmd64 {
     )
   }
 
-  fn must_wrap_return_value_in_typed_array(&self, rv: NativeType) -> bool {
+  fn must_wrap_return_value_in_typed_array(&self, rv: &NativeType) -> bool {
     // V8 only supports i32 and u32 return types for integers
     // We support 64 bit integers by wrapping them in a TypedArray out parameter
     crate::dlfcn::needs_unwrap(rv)
@@ -607,7 +616,7 @@ impl Aarch64Apple {
     let mut compiler = Self::new();
 
     let must_wrap_return_value =
-      compiler.must_wrap_return_value_in_typed_array(sym.result_type);
+      compiler.must_wrap_return_value_in_typed_array(&sym.result_type);
     let must_save_preserved_register = must_wrap_return_value;
     let cannot_tailcall = must_wrap_return_value;
 
@@ -619,14 +628,14 @@ impl Aarch64Apple {
       }
     }
 
-    for param in sym.parameter_types.iter().copied() {
+    for param in sym.parameter_types.iter().cloned() {
       compiler.move_left(param)
     }
     if !compiler.is_recv_arg_overridden() {
       // the receiver object should never be expected. Avoid its unexpected or deliberate leak
       compiler.zero_first_arg();
     }
-    if compiler.must_wrap_return_value_in_typed_array(sym.result_type) {
+    if compiler.must_wrap_return_value_in_typed_array(&sym.result_type) {
       compiler.save_out_array_to_preserved_register();
     }
 
@@ -963,7 +972,7 @@ impl Aarch64Apple {
     let mut int_params = 0u32;
     let mut float_params = 0u32;
     let mut stack_size = 0u32;
-    for param in symbol.parameter_types.iter().copied() {
+    for param in symbol.parameter_types.iter().cloned() {
       match param.into() {
         Float(float_param) => {
           float_params += 1;
@@ -1069,10 +1078,10 @@ impl Aarch64Apple {
   }
 
   fn must_save_preserved_register_to_stack(&mut self, symbol: &Symbol) -> bool {
-    self.must_wrap_return_value_in_typed_array(symbol.result_type)
+    self.must_wrap_return_value_in_typed_array(&symbol.result_type)
   }
 
-  fn must_wrap_return_value_in_typed_array(&self, rv: NativeType) -> bool {
+  fn must_wrap_return_value_in_typed_array(&self, rv: &NativeType) -> bool {
     // V8 only supports i32 and u32 return types for integers
     // We support 64 bit integers by wrapping them in a TypedArray out parameter
     crate::dlfcn::needs_unwrap(rv)
@@ -1120,9 +1129,9 @@ impl Win64 {
     let mut compiler = Self::new();
 
     let must_cast_return_value =
-      compiler.must_cast_return_value(sym.result_type);
+      compiler.must_cast_return_value(&sym.result_type);
     let must_wrap_return_value =
-      compiler.must_wrap_return_value_in_typed_array(sym.result_type);
+      compiler.must_wrap_return_value_in_typed_array(&sym.result_type);
     let must_save_preserved_register = must_wrap_return_value;
     let cannot_tailcall = must_cast_return_value || must_wrap_return_value;
 
@@ -1133,7 +1142,7 @@ impl Win64 {
       compiler.allocate_stack(&sym.parameter_types);
     }
 
-    for param in sym.parameter_types.iter().copied() {
+    for param in sym.parameter_types.iter().cloned() {
       compiler.move_left(param)
     }
     if !compiler.is_recv_arg_overridden() {
@@ -1147,7 +1156,7 @@ impl Win64 {
     if cannot_tailcall {
       compiler.call(sym.ptr.as_ptr());
       if must_cast_return_value {
-        compiler.cast_return_value(sym.result_type);
+        compiler.cast_return_value(&sym.result_type);
       }
       if must_wrap_return_value {
         compiler.wrap_return_value_in_out_array();
@@ -1284,7 +1293,7 @@ impl Win64 {
     x64!(self.assmblr; xor ecx, ecx);
   }
 
-  fn cast_return_value(&mut self, rv: NativeType) {
+  fn cast_return_value(&mut self, rv: &NativeType) {
     let s = &mut self.assmblr;
     // V8 only supports 32bit integers. We support 8 and 16 bit integers casting them to 32bits.
     // Section "Return Values" of the Windows x64 Calling Convention doc:
@@ -1419,7 +1428,7 @@ impl Win64 {
     self.params > 0
   }
 
-  fn must_cast_return_value(&self, rv: NativeType) -> bool {
+  fn must_cast_return_value(&self, rv: &NativeType) -> bool {
     // V8 only supports i32 and u32 return types for integers
     // We support 8 and 16 bit integers by extending them to 32 bits in the trampoline before returning
     matches!(
@@ -1428,7 +1437,7 @@ impl Win64 {
     )
   }
 
-  fn must_wrap_return_value_in_typed_array(&self, rv: NativeType) -> bool {
+  fn must_wrap_return_value_in_typed_array(&self, rv: &NativeType) -> bool {
     // V8 only supports i32 and u32 return types for integers
     // We support 64 bit integers by wrapping them in a TypedArray out parameter
     crate::dlfcn::needs_unwrap(rv)
@@ -1510,6 +1519,7 @@ impl From<NativeType> for Param {
       NativeType::I32 => Int(I(DW)),
       NativeType::I64 | NativeType::ISize => Int(I(QW)),
       NativeType::Buffer => Int(Buffer),
+      NativeType::Struct(_) => unimplemented!(),
     }
   }
 }

test_ffi/src/lib.rs

@@ -485,3 +485,61 @@ pub static static_char: [u8; 14] = [
   0xC0, 0xC1, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF,
   0x00,
 ];
+
+#[derive(Debug)]
+#[repr(C)]
+pub struct Rect {
+  x: f64,
+  y: f64,
+  w: f64,
+  h: f64,
+}
+
+#[no_mangle]
+pub extern "C" fn make_rect(x: f64, y: f64, w: f64, h: f64) -> Rect {
+  Rect { x, y, w, h }
+}
+
+#[no_mangle]
+pub extern "C" fn print_rect(rect: Rect) {
+  println!("{:?}", rect);
+}
+
+#[derive(Debug)]
+#[repr(C)]
+pub struct Mixed {
+  u8: u8,
+  f32: f32,
+  rect: Rect,
+  usize: usize,
+  array: [u32; 2],
+}
+
+/// # Safety
+///
+/// The array pointer to the buffer must be valid and initalized, and the length must
+/// be 2.
+#[no_mangle]
+pub unsafe extern "C" fn create_mixed(
+  u8: u8,
+  f32: f32,
+  rect: Rect,
+  usize: usize,
+  array: *const [u32; 2],
+) -> Mixed {
+  let array = *array
+    .as_ref()
+    .expect("Array parameter should contain value");
+  Mixed {
+    u8,
+    f32,
+    rect,
+    usize,
+    array,
+  }
+}
+
+#[no_mangle]
+pub extern "C" fn print_mixed(mixed: Mixed) {
+  println!("{:?}", mixed);
+}

test_ffi/tests/ffi_types.ts

@@ -66,17 +66,10 @@ const remote = Deno.dlopen(
 
 Deno.dlopen(
   "dummy_lib_2.so",
-  // is declared using "pointer" or "function" + UnsafeFnPointer
   {
     wrong_method1: {
       parameters: [],
-      // @ts-expect-error not assignable to type 'NativeResultType'
+      result: "function",
-      result: {
-        function: {
-          parameters: [],
-          result: "void",
-        },
-      },
     },
   },
 );

test_ffi/tests/integration_tests.rs

@@ -127,6 +127,10 @@ fn basic() {
     Static i64: -1242464576485\n\
     Static ptr: true\n\
     Static ptr value: 42\n\
+    Rect { x: 10.0, y: 20.0, w: 100.0, h: 200.0 }\n\
+    Rect { x: 10.0, y: 20.0, w: 100.0, h: 200.0 }\n\
+    Rect { x: 20.0, y: 20.0, w: 100.0, h: 200.0 }\n\
+    Mixed { u8: 3, f32: 12.515, rect: Rect { x: 10.0, y: 20.0, w: 100.0, h: 200.0 }, usize: 12456789, array: [8, 32] }\n\
     arrayBuffer.byteLength: 4\n\
     uint32Array.length: 1\n\
     uint32Array[0]: 42\n\

test_ffi/tests/test.js

@@ -3,7 +3,7 @@
 
 // Run using cargo test or `--v8-options=--allow-natives-syntax`
 
-import { assertEquals, assertNotEquals } from "https://deno.land/std@0.149.0/testing/asserts.ts";
+import { assertEquals, assertInstanceOf, assertNotEquals } from "https://deno.land/std@0.149.0/testing/asserts.ts";
 import {
   assertThrows,
   assert,
@@ -37,6 +37,12 @@ assertThrows(
   "Failed to register symbol non_existent_symbol",
 );
 
+const Point = ["f64", "f64"];
+const Size = ["f64", "f64"];
+const Rect = ["f64", "f64", "f64", "f64"];
+const RectNested = [{ struct: Point }, { struct: Size }];
+const Mixed = ["u8", "f32", { struct: Rect }, "usize", { struct: ["u32", "u32"] }];
+
 const dylib = Deno.dlopen(libPath, {
   "printSomething": {
     name: "print_something",
@@ -210,6 +216,34 @@ const dylib = Deno.dlopen(libPath, {
     type: "pointer",
   },
   "hash": { parameters: ["buffer", "u32"], result: "u32" },
+  make_rect: {
+    parameters: ["f64", "f64", "f64", "f64"],
+    result: { struct: Rect },
+  },
+  make_rect_async: {
+    name: "make_rect",
+    nonblocking: true,
+    parameters: ["f64", "f64", "f64", "f64"],
+    result: { struct: RectNested },
+  },
+  print_rect: {
+    parameters: [{ struct: Rect }],
+    result: "void",
+  },
+  print_rect_async: {
+    name: "print_rect",
+    nonblocking: true,
+    parameters: [{ struct: Rect }],
+    result: "void",
+  },
+  create_mixed: {
+    parameters: ["u8", "f32", { struct: Rect }, "pointer", "buffer"],
+    result: { struct: Mixed }
+  },
+  print_mixed: {
+    parameters: [{ struct: Mixed }],
+    result: "void",
+  },
 });
 const { symbols } = dylib;
 
@@ -571,6 +605,46 @@ console.log(
 const view = new Deno.UnsafePointerView(dylib.symbols.static_ptr);
 console.log("Static ptr value:", view.getUint32());
 
+// Test struct returning
+const rect_sync = dylib.symbols.make_rect(10, 20, 100, 200);
+assertInstanceOf(rect_sync, Uint8Array);
+assertEquals(rect_sync.length, 4 * 8);
+assertEquals(Array.from(new Float64Array(rect_sync.buffer)), [10, 20, 100, 200]);
+// Test struct passing
+dylib.symbols.print_rect(rect_sync);
+// Test struct passing asynchronously
+await dylib.symbols.print_rect_async(rect_sync);
+dylib.symbols.print_rect(new Float64Array([20, 20, 100, 200]));
+// Test struct returning asynchronously
+const rect_async = await dylib.symbols.make_rect_async(10, 20, 100, 200);
+assertInstanceOf(rect_async, Uint8Array);
+assertEquals(rect_async.length, 4 * 8);
+assertEquals(Array.from(new Float64Array(rect_async.buffer)), [10, 20, 100, 200]);
+
+// Test complex, mixed struct returning and passing
+const mixedStruct = dylib.symbols.create_mixed(3, 12.515000343322754, rect_async, 12456789, new Uint32Array([8, 32]));
+assertEquals(mixedStruct.length, 56);
+assertEquals(Array.from(mixedStruct.subarray(0, 4)), [3, 0, 0, 0]);
+assertEquals(new Float32Array(mixedStruct.buffer, 4, 1)[0], 12.515000343322754);
+assertEquals(new Float64Array(mixedStruct.buffer, 8, 4), new Float64Array(rect_async.buffer));
+assertEquals(new BigUint64Array(mixedStruct.buffer, 40, 1)[0], 12456789n);
+assertEquals(new Uint32Array(mixedStruct.buffer, 48, 2), new Uint32Array([8, 32]));
+dylib.symbols.print_mixed(mixedStruct);
+
+const cb = new Deno.UnsafeCallback({
+  parameters: [{ struct: Rect }],
+  result: { struct: Rect },
+}, (innerRect) => {
+  innerRect = new Float64Array(innerRect.buffer);
+  return new Float64Array([innerRect[0] + 10, innerRect[1] + 10, innerRect[2] + 10, innerRect[3] + 10]);
+});
+
+const cbFfi = new Deno.UnsafeFnPointer(cb.pointer, cb.definition);
+const cbResult = new Float64Array(cbFfi.call(rect_async).buffer);
+assertEquals(Array.from(cbResult), [20, 30, 110, 210]);
+
+cb.close();
+
 const arrayBuffer = view.getArrayBuffer(4);
 const uint32Array = new Uint32Array(arrayBuffer);
 console.log("arrayBuffer.byteLength:", arrayBuffer.byteLength);